In a 1- to 2-quart pan, whisk sugar, cornstarch, instant espresso, cinnamon, chocolate, and 1/2 cup milk to blend. Whisking, bring to a boil over medium-high heat, 3 to 4 minutes. If sauce is too thick to drizzle, stir in more milk, 1 tablespoon at a time. Use hot or warm.
Nutritional analysis per tablespoon.